1. Field of the Invention
The present invention relates to an analytical method for multi-component aqueous solutions and an apparatus for the same, and, in particular, to a method for determining concentration values of a plurality of components from a near-infrared absorption spectrum and an apparatus for the same, which method and apparatus are used in fields such as semiconductor processing and food processing.
2. Description of the Prior Art
In an analytical system for determining concentrations of a multi-component aqueous solution by the use of a spectrophotometer, absorbance (optical absorptivities) has been measured at absorptive wavelengths inherent to the respective components, and their values have been compared with known calibration curves previously obtained for standard samples, as shown in, for example, FIGS. 12(A) and (B), to determine concentrations.
In such an analytical system as shown in FIG. 13, in order to make a temperature of the multi-component aqueous solution of unknown concentrations to be measured equal to a liquid temperature of the standard solution at a calibration time, the multi-component aqueous solution (x.degree. C.) within a chemical tank 16 has been introduced into a flow cell 10 through a thermostatic bath 13 (e.g., 25.degree. C.), as shown in FIG. 13. In addition, reference numeral 1 designates a light source and reference numeral 18 designates a spectrometer (near-infrared spectral and detecting means).
However, in the above-described analytical system on the basis of the calibration curves, a disadvantage is present in that the accuracy of the measurement is remarkably lowered by interferences due to other components. In particular, absorbance ranges of an aqueous solution are overlapped within a near-infrared range in many cases, so that it has been difficult to eliminate influences due to other components, and it has also been considerably troublesome to draw calibration curves.
In addition, in a process using high-temperature chemicals, if chemicals cooled in the thermostatic bath 13 are returned to the chemical tank 16, a deviation from processing conditions has occurred according to such circumstances. Moreover, the thermostatic bath 13 and temperature-adjusting means 17 therefor are bulky, so that the apparatus is large so that not only is a wide installation area required but also the apparatus is complicated and expensive.